The present invention describes a bioabsorbable layered surgical implant comprising two components. One component is a solid plate of bioabsorbable polymer and the other is a web made of bioabsorbable fibers. These implants guide and enhance bone healing and protect the soft tissues beneath the healing bone. These implants are particularly useful in cranioplasty.
Guided bone regeneration by means of implants has a long history, especially in cranioplasty, where there exists a great need to prevent damage to the brain by covering holes and other defects in cranial bone. The materials used to effect guided bone regeneration, such as would occur in cranioplasty, must meet several criteria. They must have, for example, good biocompatibility and high mechanical strength. Further, they should not cause bone erosion.
In the past, bone tissue grafts have been made, for example, as allografts from canine bone, human bone, decalcified bone, pericranium, and as autografts from the tibia, rib and crista iliac. See Zeiss Index and History of Plastic Surgery 900 BC-1863 AD Baltimore, Williams and Wilkins, 1977, vol 1, pp 51-52; Chase S. W., Herndon C. H., The fate of autogenous and homogenous bone grafts: A historical review, Journal of Bone Joint Surgery 37 A, 1955, pp. 809-841; Prolo D. J., Cranial defects and cranioplasty, in Wilkins R H, Rengachary S S (eds): Neurosurgery, New York, McGraw-Hill, 1984, pp 1647-1656; Grant F. C., Norcross N. C., Repair of Cranial Defects By Cranioplasty, Annual Surgery vol. 110, 1939, pp. 488-512; Reeves D. L., Cranioplasty, Springfield Ill., Charles C. Thomas, 1950; and Woolf J. I., Walker A. E., Cranioplasty, Collective review, International Abstracts Surgery 81, 1945, pp. 1-23, the entire disclosures of each of which are incorporated herein by way of this reference. However, there are problems associated with the use of bone tissue grafts. If the patient""s own bone is used as a graft, a surgeon must perform an additional, traumatic operation to take the bone sample. If the bone graft is taken from another person or animal bone is used, viral contaminations or immunological problems are possible, even if the graft is treated to make it compatible with the patient""s tissue.
Additionally, man-made biostable materials have been studied in cranioplasty applications, such as cellulose fibers, aluminum, gold, titanium, stainless steel, poly methyl methacrylate (PMMA), polyethylene and silicone. See, Habal M. B., Leake D. L., Maniscako J. E., A new method for reconstruction of major defects in the cranial vault, Surgery Neurology 6, 1976, pp. 137-138; Karvounis P. C., Chiu J., Sabin H., The use of prefabricated polyethylene plate for cranioplasty, Journal of Trauma 10, 1970, pp. 249-254; and Black S. P. W., Reconstruction of the supraorbital ridge using aluminum, Surgery Neurology 9, 1978, pp. 121-128, the entire disclosures of each of which are incorporated herein by way of this reference. However, the clinical use of most of these materials has been rejected due to severe tissue reactions. Further, biostable implants are particularly ill-suited for cranioplasty in children because a biostable implant prevents the immature skull bone from growing to adult size and, therefore, the implant needs to be removed in a second surgical procedure.
Many of the problems of biostable materials can be solved with implants made of bioabsorbable polymers, which cause fewer inflammatory reactions. The bioabsorbable implants are also suitable for children, because these implants resorb totally and the degradation products disappear from the body via metabolic routes. Moreover, these materials can be chosen to degrade quickly enough so that the growth of the child""s cranium is not restricted, thereby obviating the need for a second operation. Even with bioabsorbable plates, however, there is a desire to effect quicker bone regeneration and healing.
Thus, it is a goal of the present invention to provide an implant, particularly for cranioplasty, that is bioabsorbable, yet strong enough to protect soft tissue, such as the brain, during the healing period.
It is further a goal of the present invention to provide an implant, particularly for cranioplasty, that may be easily shaped or formed and applied over a defect in a bone, such as the cranium.
It is further a goal of the present invention to provide an implant, particularly for cranioplasty, that will promote quick bone regeneration, thereby shortening the healing period.
It is further a goal of the present invention to provide an implant, particularly for cranioplasty, that will degrade quickly enough so as not to restrict the natural growth in children of the bone under repair.
These and other goals are met with the present invention, comprising a rigid and tough, yet easily shaped, layered bioabsorbable implant for guided bone tissue regeneration, which may be used as a bioabsorbable surgical cranioplasty implant. The implant described in more detail in this application comprises two components. One component is a solid plate of a bioabsorbable polymer and the other is a web, typically made of bioabsorbable fibers. These implants have a surface structure that promotes bone growth on one side and prevents tissue irritation on the other. Thus, implants of the present invention enhance bone healing and protect the soft tissues beneath the healing bone and around the implant.